The present invention relates to an ink ribbon for use with an output device such as a thermal printer, and more particularly to a color ink ribbon having a plurality of color ink layers alternately arranged, so as to carry out desired color printing.
Conventionally, there is known such a color thermal printer using a color ink ribbon having a plurality of color ink layers alternately arranged so as to carry out desired color printing.
FIGS. 3A and 3B show a conventionaI color ink ribbon for use with such a color thermal printer. A color ink ribbon 1 includes a base 2 formed of a light transmitting material such as polyethylene terephthalate (PETP) and a plurality of ink layers 3A, 3B, 3C . . (which will be hereinafter generally referred to as ink layers 8) having different colors. The ink layers are formed on the base 2 in such a manner as to be arranged longitudinally of the color ink ribbon 1 at internals. The color ink ribbon 1 further includes a plurality of colored markers 4 formed on the base 2 for discriminating the colors of the ink layers 3 with a color sensor 10 to be hereinafter described. Each marker 4 is located upstream of each ink layer 3 in a moving direction of the color ink ribbon 1 in such a manner as to be longitudinally spaced from the adjacent ink layers 3. The markers 4 have different lengths corresponding to the colors of the ink layers 3 located just downstream of the markers 4 in the moving direction of the color ink ribbon 1. The provision of the spaces between each marker 4 and the adjacent ink layers 3 is intended to prevent that when the lengths of the markers 4 are sensed by the color sensor -0 to discriminate the colors corresponding to the markers 4, the color sensor 10 would erroneously sense the ink layers 3 adjacent the markers 4 if the ink layers 3 and the markers 4 were arranged side by side.
FIG. 4 shows an essential part of the thermal printer for carrying out color printing by using the above color ink ribbon 1. The thermal printer includes a cylindrical platen 12 fixed on a rotating shaft 11. A pair of parallel support shafts 13 and 14 are arranged on the front side of the platen 12 fur supporting a carriage 15 movable along an axial direction of the platen 12. The carriage 15 is connected to a wire (not shown) adapted to be moved through rotation of pulleys by driving a motor. Thus the carriage 15 Is adapted to be reciprocated along the platen 12 while being supported to the support shafts 13 and 14.
The carriage 15 is provided with a thermal head 16 opposed to the platen 12. A ribbon cassette 17 including the color ink ribbon 1 wound around a pair of spools 18 and 19 is mounted in the carriage 15. The color ink ribbon 1 is exposed outside at an intermediate position between the spools 18 and 19. The color ink ribbon 1 exposed from the ribbon cassette 17 and a paper 20 are sandwiched between the thermal head 16 and the platen 12. In printing operation, a plurality of heat generating elements of the thermal head 16 are selectively activated while moving the carriage 15, thereby melting the ink layers 3 of the color ink ribbon 1 and transferring the molten ink layers 3 onto the paper 20. The color sensor 10 for discriminating the colors of the ink layers 3 with the markers 4 of the color ink ribbon 1 is mounted on the thermal head 16. As shown In FIG. 5, the color sensor 10 comprises a support block 21 having a central groove 22, a light emitting device 23 and a light receiving device 24. The light emitting device 23 and the light receiving device 24 are arranged in opposed relationship to each other on opposite sides of the central groove 22. The color ink ribbon 1 is adapted to pass through the central groove 22 at a uniform speed. Light emitted from the light emitting device 23 is received by the light receiving device 24, and the light is blocked by the markers 4 having different lengths during running of the ink ribbon 1 for different periods of time. Accordingly, these periods of time are detected to discriminate the colors of the ink layers 3 just downstream of the markers 4.
When the thermal head 16 is moved at a uniform speed under the condition that the color ink ribbon 1 exposed from the ribbon cassette 17 and the paper 20 are sandwiched between the thermal head 16 and the platen 12, the color ink ribbon 1 is taken out from the spool 18 in such a manner that slippage of the color ink ribbon 1 may not generated owing to a frictional force between the color ink ribbon 1 and the paper 20. During running of the color ink ribbon 1, the color sensor 10 operates to detect the color of each ink layer 3 according to the length of each marker 4, and when the ink layer 3 of a desired color to be printed reaches a position opposed to the thermal head 16, the plurality of heat generating elements of the thermal head 16 are selectively activated to melt the molten the ink layer 3 and thereby transfer the molten ink of the ink layer 3 onto the paper 20. Thus, the color printing is carried out.
In the conventional color ink ribbon 1 as mentioned above, the base 2 is exposed between each marker 4 and each ink layer 3. The base 2 is formed of a material having a low coefficient of friction such as polyethylene terephthalate as mentioned above. Therefore, when the base 2 is opposed to the paper 20, there is a possibility of the color ink ribbon 1 as well as the thermal head 16 being slid relative to the paper 20. If the color ink ribbon 1 is slid relative to the paper 20, the ink layer 3 cannot reach a position opposed to the thermal head 16 within a predetermined period of time after the color sensor 10 discriminates the color of the ink layer 3 with the corresponding marker 4 of the color ink ribbon 1. As a result, a leading edge of each ink layer 3 cannot be precisely positioned to cause deterioration of printing quality.